Category Archives: Sawflies

Ornamental Pest, Sawflies, Shrubs

What’s Eating My Roses in Spring? — Sawflies

If you’re seeing insect damage on your roses this spring, you aren’t alone and there are a number of early-season insect that can catch our attention.  For example, a number of caterpillars can occasionally be spotted on roses in spring, such as the rose plume moth (Cnaemidophorus rhododactyla).  There’s also the non-native rose leafhopper (Edwardsiana rosae) which can cause faint speckling on leaves. Later in the growing season, rose chafers (Macrodactylus subspinosus) and the notorious Japanese beetle (Popillia japonica) can be a concern.

Perhaps the most noticeable damage to roses in spring is caused by the larvae of sawflies.  These insects cause two types of damage: “windowpane” damage when they only feed partway through foliage and leave the upper leaf surface intact or small holes or notches when larger larvae chew entirely through the leaves.  In the Midwest, there are three different species of sawflies that can commonly be encountered on roses in spring: the roseslug sawfly (Endelomyia aethiops), the curled rose sawfly (Allantus cinctus), and the bristly roseslug sawfly (Claudius diffiformis).  To the naked eye, the larvae (up to ~ ½ inch long, pale greenish, and caterpillar-like) and the adults (~ ⅓ inch long, dark-colored, and wasp-like) all look similar.  However, determining the exact species under magnification can be helpful to understand the potential impacts on your roses.

Classic “windowpane” damage caused by sawfly larvae on roses. This damage occurs when small sawfly larva only feed partway through the leaves. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

The roseslug sawfly (Endelomyia aethiops) is the commonest of the three sawflies that I see samples of at the UW Insect Diagnostic Lab.  The larvae of this species have a smooth texture and brownish head capsule; their bodies are translucent and they usually have a pale greenish color due to ingested green leaf material.  Some good news about the roseslug sawfly is that this species only has a single generation in spring.  Their damage tends to be mostly just a minor cosmetic issue.  As the plants really take off in late spring, they tend to “shrug off” this damage and it’s quickly covered up by new growth.

Larva of the roseslug sawfly (Endelomyia aethiops) feeding on the underside of a rose leaf. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

The curled rose sawfly (Allantus cinctus) goes through two generations early in the growing season.  Similar to the roseslug sawfly, their feeding damage tends to be minor and plants are usually able to chug along just fine.  The larvae of the curled rose sawfly also are pale green with a brownish-orange head capsule.  They do have tiny spots on their bodies, but these are only visible under high magnification.  This species tends to feed while curled up and they also chew notches on the edges of leaves which can help distinguish this species from the other two sawflies.

Larva of a curled rose sawfly (Allantus cinctus) on the underside of a rose leaf. Note the notches on the edges of leaves which can serve as a clue to help identify this species. A rose leafhopper nymph is also present to the left of the larva. Photo credit: PJ Liesch, UW Insect Diagnostic Lab

The third sawfly commonly seen on roses also tends to be the most problematic—the bristly roseslug sawfly (Claudius diffiformis).  Unlike the first two sawflies, this one can continue to reproduce throughout the growing season.  Because they go through many generations per year, their damage can accumulate over time and tends to be more notable.  Like the other two sawflies, the larvae of this species are also pale green with a brownish head capsule, but they are covered with fine, hair-like bristles when viewed under magnification.  Very few sawflies have a hairy or bristly appearance like this, which helps distinguish this species on roses.

Larva of the bristly roseslug sawfly (Claudius diffiformis). Note the fine hair-like bristles which help identify this species as seen in this magnified photo. Photo credit: PJ Liesch, UW Insect Diagnostic Lab.

If you do bump into these sawflies on your roses in spring, they’re pretty easy to deal with.  Options for managing them include:

  1. Do nothing. Since damage from the roseslug and curled rose sawflies tend to be minor, established plants often tolerate these insects with little/no intervention.
  2. Squishing, hand-picking or knocking them into a container of soapy water (be mindful of thorns…)
  3. Insecticidal soap or horticultural oils such as neem oil.  Make sure to achieve good spray coverage.
  4. Pyrethrins or spinosad—both are organic spray options. Note that Bacillus thuringiensis kurstaki (which works well against caterpillars) does not work against these sawflies.
  5. Conventional sprays from the hardware store/garden center labelled for use on ornamental shrubs and landscape plants.  Use caution since these products tend to have broader-spectrum of activity and can pose greater risks to bees and other pollinators such as butterflies, moths, beetles, and many flies.

  

Butterflies, Caterpillars, Crop Pests, Medical Entomology, Moths, Ornamental Pest, Pollinators, Sawflies, Shrubs

2018’s Top Trends from the Diagnostic Lab (Part 2)

In this post, we’re continuing to count down the University of Wisconsin Insect Diagnostic Lab’s top arthropod trends of 2018. This is the second half of a two part series; the first half can be found here.

5) White-Lined and Other Sphinx Moths:
The white-lined sphinx moth (Hyles lineata) can be a common species, so encountering one of the 3 inch long hornworm caterpillars isn’t unusual. However, these caterpillars can also be encountered in massive road-traversing hordes if the conditions are just right. From midsummer onwards, large numbers of these caterpillars were observed around the state—in some cases by the tens of thousands. If you didn’t spot any of the caterpillars themselves, you might have encountered the large adult moths with their hummingbird-like behaviour in late summer. Several other sphinx moths species also had a strong presence in 2018, such as the clearwing hummingbird moths and the tobacco and tomato hornworm caterpillars which can regularly be encountered in gardens as they munch away on tomato and pepper plants.

Large, dark-colored hornworm caterpillar of the white-lined sphinx moth on a plant
Large, dark-colored hornworm caterpillar of the white-lined sphinx moth. Photo submitted by Ted Bay, UW-Extension

4) Sawflies:
Sawflies, the caterpillar copycats of the insect world, are a diverse group, so they’re always present to some extent. Last year saw an unexpected abundance of two particular types in Wisconsin—the dogwood sawfly and the non-native Monostegia abdominalis, which feeds on creeping Jenny and related plants from the loosestrife group (Lysimachia species). While sawflies are plant feeders, dogwood sawflies can also damage the soft wood of a home’s siding or trim when these insects excavate small chambers to pupate in. The UW Insect Diagnostic Lab saw a distinct bump in reports of wood damage from the dogwood sawfly last year.

Whitish larva of the dogwood sawfly curled up on a dogwood leaf
Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

3) Armyworms:
True armyworms (Mythimna unipuncta) can be a dynamic and sporadic pest in the Midwest. This species doesn’t survive the cold winters of our area, so adult armyworm moths must invade from the south each spring. Depending on national weather patterns, the arrival of the adult moths can vary significantly from year to year. If an early mass arrival is followed by abundant food and ideal conditions for the ensuing caterpillars, large populations can result. Once they’ve arrived, true armyworms can go through 2-3 generations in the state and this second generation of caterpillars made an alarming appearance in mid-to-late July. Under the conditions last summer, massive hordes of these caterpillars decimated crop fields before marching across roads by the tens or hundreds of thousands to look for their next meal. In some cases, that next meal included turfgrass, meaning that some Wisconsinites came home from work to biblical hordes of caterpillars and half-eaten lawns in late July.

Striped caterpillar of the true armyworm
Caterpillar of the True Armyworm (Mythimna unipuncta). Photo Credit: Lyssa Seefeldt, University of Wisconsin-Madison Extension

2) Monarch Butterflies:
Much to the delight of fans and conservationists, the iconic monarch butterfly (Danaus plexippus) appeared to have a banner year in the Midwest in 2018. Reports and observations of high numbers of monarchs poured into the Insect Diagnostic Lab during the summer months. As comforting as these reports were, the butterflies still faced a perilous 2,000 mile journey to reach their overwintering grounds in Mexico.  The most consistent measurement of the eastern monarch population comes from estimating the area occupied by the densely-packed overwintering butterflies.  In late January the latest count was released with encouraging news—the eastern monarch population is up 144% over last year and is estimated to be the largest in over a decade.  In contrast, the western monarch population overwinters in southern California and has recently dipped to alarmingly low numbers. Regardless of the winter assessments, monarchs face tough challenges and Wisconsinites are encouraged to help conserve this iconic species.  The Wisconsin Monarch Collaborative recently launched a website with resources for those wishing to join the effort.

Seven monarch butterflies nectaring on a flower
Multiple monarch butterflies nectaring on a single plant in August. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

1) Floodwater Mosquitoes:
Mosquitoes snagged the top spot on 2018’s list for good reason. The upper Great Lakes region is home to over 60 different mosquito species, but one subset—the “floodwater” mosquitoes—drove the storyline last year and impacted outdoor activities through much of the spring and summer months. Mosquitoes in this group, such as the inland floodwater mosquito (Aedes vexans), flourish when heavy rains come. Last year’s mosquito season kicked off in force with a batch of pesky and persistent floodwater mosquitoes just before Memorial Day weekend. Mosquito monitoring traps in southern Wisconsin captured record numbers of mosquitoes shortly thereafter. Later in the year, the Midwest experienced an unprecedented series of severe rainstorms, setting the stage for an encore performance of these mosquitoes. It was this second explosion of mosquitoes that caught the attention of anyone trying to enjoy the outdoors in late summer—a time of the year when mosquitoes are typically winding down in the state.

Ephemeral pools of water created ideal conditions for floodwater mosquitoes in late summer. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab
Borers, Ornamental Pest, Outdoor Worms, Sawflies, Wood-attacking Insects

A Wood-Boring Insect Mystery

Imagine it’s August and as you wander in from your backyard, you notice a small pile of sawdust at the bottom of the door frame.  It might not be much sawdust, but you also find a few holes in the wood trim nearby.  It definitely seems to be insect damage, but who’s the culprit?

Unexpected insect damage to wood trim.

If you came up with a list of insects in the upper Midwest that can damage the wood of your home, it wouldn’t be terribly long.  For good reason, termites might be the first insect to come to mind, although our eastern subterranean termites are restricted to isolated pockets and are not commonly encountered in Wisconsin.  A close second on the list might be carpenter ants.  Interestingly, carpenter ants don’t technically eat (e.g., digest) wood and merely excavate soft, rotting wood to create a nesting site.  If anything, their presence in a home might be an indicator of a water damage.  Powderpost beetles can also attack wood and are commonly encountered in old barn beams and log cabins.  Carpenter bees help round out a list of the “usual suspects”.  These wood-boring bees can create good sized holes (a half inch across), although with their preference for unpainted softwoods used for trim, siding, and fence posts, their damage is mostly cosmetic in nature. 

Then another clue comes to mind—the nearby shrubs that had been eaten by some kind of worm-like insect over the past few weeks. 

Larva of a dogwood sawfly showing the whitish, waxy coating. Photo Credit: PJ Liesch, UW Insect Diagnostic Lab

When it comes to wood-damaging pests, sawflies generally don’t come to mind.  Sawfly larvae—Mother Nature’s caterpillar copycats—tend to feed on plant leaves.  Species like the European pine sawfly, dusky birch sawfly, rose slug sawfly, Columbine sawfly, pearslug sawfly, and birch leafminer sawfly can all be commonly encountered feeding on plants during the growing season.  One species that was common in 2018—the dogwood sawfly—is unique in that it not only causes plant damage but can also damage wood trim and siding of homes.  The dogwood sawfly is one of our commonest pests of native and landscape dogwoods (Cornus spp.).  When larvae are small,  they have a whitish waxy coating thought to mimic bird droppings and they can often be found curled up on the undersides of dogwood leaves.  As larvae mature, they lose the waxy coating and their black and yellow coloration becomes conspicuous.   

Mature dogwood sawfly larva with classic black and yellow appearance.

So how does this plant-feeding species end up damaging wood?  As is the case with any insect that undergoes complete metamorphosis, the larvae need to pass through the pupal stage to make it to adulthood. Insect pupae, however, are generally immobile can make an an easy meal for any predator that stumbles upon them.  Thus, many insects seek out tucked away spots to complete their pupal stage.  When ready to pupate, dogwood sawfly larvae typically create their own hideaway by chewing small chambers in rotting wood such as twigs, branches, or logs near the shrub they had been feeding on. 

Small chambers chewed into a fallen twig—a “typical” spot for dogwood sawfly to pupate.

If rotting wood is unavailable, the larvae may turn to other nearby wood materials—including wood trim and siding.  This typically occurs when larvae had been feeding on ornamental dogwood shrubs planted close to a home.  In the grand scheme of things, these insects don’t cause that much damage to wood, although homeowners won’t be thrilled if they’ve been caught off guard by this unexpected wood-damaging pest! 

Ornamental Pest, Outdoor Worms, Sawflies

Sawflies: Caterpillar Copycats

As the old saying goes: if it looks like a duck, swims like a duck, and quacks like a duck, it’s probably a duck.  Following that logic: if it looks like a caterpillar, walks like a caterpillar,  and feeds on plants like a caterpillar, it’s probably a caterpillar—right?

This isn’t always the case and one important example would be the sawflies.  Sawfly larvae look an awful lot like true caterpillars (which turn into moths or butterflies), but these creatures are actually related to ants, bees and wasps.  In contrast, adult sawflies have a distinct wasp-like appearance which hints at the true evolutionary relationships of these creatures.

Elm sawfly adult. The wasp-like appearance reflects the relationship of sawflies to ants, bees, and wasps.

With a little know-how, you can learn to tell apart sawfly larvae from true caterpillars. In addition to three pairs of true jointed legs on the thorax, true caterpillars possess 4-5 pairs (or fewer for “inchworms”) of stubby, blob-like prolegs on their abdomen—each tipped with tiny velcro-like hooks (crochets) that can be seen under magnification.  Sawflies have more pairs of prolegs (7 pairs) and lack crochets.

Larva of the dogwood sawfly. Note the strong resemblance to a caterpillar, but this larva has seven pairs of stubby prolegs on the abdomen.

There are dozens of sawfly species in the Midwest, some of which can be considered plant pests, while others can go unnoticed due to their small size or cryptic habits.  The commonest sawfly species can be pests of pines and other conifers, elms, birches, and other hardwoods, and ornamental flowers and shrubs such as dogwoods, roses, and columbines.  If you’ve ever spent time thumbing through a caterpillar guide book and can’t seem to find a match, there’s always a chance you might be looking at a sawfly.

To further explore the world of sawflies, check out this article from the Wisconsin Master Gardener Program.